Heat treatment of large manganese-steel shapes.



WINFIELI) S. POTTER, OF NEW YORK, N. Y.

HEAT TREATMENT OF LARGE MANGANESE-STEEL SHAPES.

No Drawing.

Specification of Letters Patent. Application filed December 29, 1911. Serial No. 668,458. I

Patented Feb. 20, 1912.

To all whom it may concern.-

Be it known that I, WINFIELD S. Po'rmn, a citizen of the United States, residing in the borough of Manhattan, city, county,

and State of New York, have invented oer-- tain new and useful Improvements in Heat Treatment of Large Manganese-Steel Shapes; and I do hereby declare the following to be a full, clear, and exact description,

of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My present invention relates to methods of producing heat-treated and toughened manganese steel products in a condition free from injurious strains and with a strong tough condition of the metal throughout the finished shape; and pertains more particularly to theproduction of such thick shapes as might not be brought when cold into a tough condition in their central-or interior portions by heat-treating as heretofore practiced and then rapidly cooling or quenching by immersing in water.

In accordance with my invention the shape is brought to a temperature which is substantially below the temperature at which quenching takes place in the ordinary practice, and which is made nearly uniform throughout the section of the shape; and during this preliminary reduction of temperature the metal is given a fine-grained, strong, wrought condition, and such condition is maintained without separations or recrystallization, by a suitable rolling, forging or working. Inthe preferred practice the shape is then rapidly cooled, but in such moderated or graduated manner as to avoid the setting up of violent or prejudicial strains in the mass, and yet so rapidly that the mass is cooled throughout, including its central or interior portions, in so short a time of total cooling and under such conditions of tension or pressure in its parts as to avoid those separations, during the cooling, which would otherwise render the manganese steel product weak and lacking in toughness.

In order to realize fully the advantages of the invention, and to give the metal prodnot a high degree of excellence, the shape is preferably produced by first heating a blank until it is in a uniform austenite condition, 2'. e., in a state of uniformity of structure and solution of its constituents, and then working the blank into the intended form and continuing the working, with intermediate reheating as may be necessary, until the metal is finally workedthroughout at;

relatively low forging or working temperatures such as 800 C. to 1000 0., and until the metal is given the desired strong finegrained condition. By working the blank until at temperatures below 1000 C. and with force or pressure applied continuously, or intermittently but at frequent intervals, the mass is brought to these relatively low temperatures without having suffered any of those detrimental changes in the structure, such as recrystallizing or separation of carbids within or between the grains of the steel, which would occur if the metal had been cooled gradually and without coincident working. The'result of this preliminary reduction of temperature with coincident working is, therefore, that'the metal is in a strong compacted condition .well adapted to resist the temporary internal stresses and strains necessarily incident to the subsequent cooling step of the operation; and the metal is, furthermore, by having been given a temperature less than the usually employed quenching temperature of manganese steel, already in part contracted. In the preferred mode of operation, the hot shape is now rapidly cooled throughout, .at least to a temperature below 420 C., but as the hot size of the shape was diminished by partial cooling and contraction before rapid cooling, the initial rapid shrinkage of the exterior portions of the mass uponits interior portions is correspondingly lessened, and the exterior portions are stretched to a. lesser degree during the early stages of the rapid coolin than if the piece had been rapidly cooled cm a higher temperature, that is, from the usually employed quenching temperature for manganese steel. also, during the latter cooling stages, the interior portions, having previously been in part cooled and contracted,'have a lesser tendency to assume a state of tension as I between the interior v at first in contact with a cooling parts and the parts exterior to them. I

In order to further minimize the stresses present during cooling, the cooling operation is conducted at first to a moderate extent by bringing the hot finished shape in contact with a cooling medium which will abstract a portion only of its surface heat and temperature, such, for example, as a bath of a melted alloy or metal (say lead or a lead tin alloy) having at the time a temperature preferably below 420 C., and the cooling is then, in the preferred operation, more rapidly or efliciently conducted by moving the piece with relation to the metal bath, having now a temperature below 420 (1, until the shape is cooled throughout to substantially the temperature of the bath. At and below this temperature the objectionable separations and recrystallization by reversion cannot take place. After this the shape may be brought down to atmospheric temperature by air cooling or in any other suitable way, since the separations and recrystallization have no longer to be guarded against. Or the same effect of a moderated initial cooling, subsequent to the working operation, followed by an increased eficiency of cooling to bring the entire mass rapidl to the desired low temperature, may be e fected by bringing the hot finished shape medium of moderate efliciency, such as an oil bath or a light water shower, for a few seconds, and

then'lncreasing the eiliciency of the cooling agent by rapidly increasing the force of impact and the quantity of the water, or like cooling agent, applied preferably as a number of suitably distributed jets, until the jets finally attain a discharge pressure of say 500 pounds per square inch; the whole cooling operation, subsequent to the working operation, be conducted in a short time, say about one minute.

By observing the above described procedure such thick shapes as balls or spheres having a diameter of say 5 inches to 12 inches may, by being first brought to thelowered and nearly uniform temperature (for example, a temperature of 800 C. to 950 C.) and then by being cooled first in a moderated manner and subsequently with greater cooling efficiency so that the entire mass is cooled throughout in a very short total time of cooling, be finally given throughout a uniform atmospheric tempera ture with a'substantial readjustment of the temporary cooling stresses so that no prejudicial strains are present and the finished product will be in a strong, tough condition throughout. In similar manner, heavy plates, such as thick plates of manganese steel, (or high manganese steel containing hardening metals, as for example, chrotion, may be produced in a strong, tough condition, free from prejudicial strains.

Although it is preferred to discontinue the preliminary reduction of temperature and coincident working at a temperature between 1000 C. and 800 (1, as above described, yet it is possible to attain good results by continuing this reduction of temperature and coincident working or pressure still further, before the final rapid cooling takes place; and it is even posslble to cool the mass entirely to a temperature below 420 C. by continuing the coincident work ing or pressure down to that temperature, and in this case the metal would suffer only slight changes, because while the pressure or working is continued, the carbids do not separate and recrystallization of the finished shape is avoided.

The production of a shape by first heating until the metal is in a uniform austenite condition may be effected, for example, in accordance with the method disclosed in my United States Letters Patent No. 97 5371 of November 8th, 1910.

Having now fully described my invention what I claim and desire to secure by Letters Patent is:

1.- The method of producing thick shapes of manganese steel in a strong tough condition substantially devoid of strains, which consists in bringing a blank of such steel into a uniform austenite condition at a suitably high working temperature, working the metal into the intended form and completing the working at temperatures between 800 and 1000 C., and then cooling by first subjecting the blank to the moderate cooling ac tion of a suitable coolin agent and subsequently increasing the eflicienoy of the cooling agent to complete the cooling to a temperature below 420 C. at such rate as to avoid separations or recrystallization within the mass; substantially as described.

2. In a method of producing a thick shape of manganese steel in a strong toughv condition substantially devoid of strains, from a blank of such steel which has previously been brought into a uniform austenite condition at a suitable high working temperature; preliminarily reducing the temperature of the blank with coincident working to avoid the separations and recrystallizations within the mass which would otherwise take place during such cooling, and completing the cooling to below 420 C. at a higher rate than is possible by immersion in still water; substantially as described.

3. The method of producing thick shapes of manganese steel in a strong tough condition substantially devoid of strains, which consists in bringing a blank of such steel into a uniform austemte condition at a suitmetal having a temperature less than 420 ably high working temperature, working the C.; substantlally as described.. 10

metal into the intended form and continu- In testimony whereof I afiix my signature, ing the working through a substantial prein presence of two witnesses. liminary'reduction of the temperature with- WINFIELD S. POTTER. out separations or recrystallization within Witnesses:

the mass, and then completing the cooling MINERVA LoBEL,

by immersing the blank in a bath of molten WILLIAM DAVIS. 

